The granuloma plays an important role in host defense against M. tuberculosis. The mechanisms that regulate the formation and maintenance of the tuberculous granuloma are, however, poorly understood. Chemokines and chemokine receptors play an essential role in cell migration in both physiological and pathophysiological states. Emerging evidence suggests a role for chemokine and chemokine receptors in regulating the granulomatous response during infection. M. tuberculosis has the ability to modulate chemokine and chemokine receptor expression in both in vitro and in vivo systems. Tumor necrosis factor-alpha (TNF-alpha) is essential for the control of tuberculosis, and is a potent regulator of chemokine expression and leukocyte trafficking. We have shown that neutralizing TNF-alpha in mice with persistent tuberculosis results in disease recrudescence associated with granuloma disorganization and diffuse cellular infiltration in the lungs. Based on these observations, we propose to test the hypotheses that: i) chemokines and chemokine receptors play an important role in orchestrating cell migration and granuloma formation in tuberculosis; and ii) TNF-alpha regulates the granulomatous response by directing the trafficking of immune cells at the site of infection via regulation of specific chemokines and chemokine receptors. Because of the importance of Type 1 T cells in host defense against M. tuberculosis, efforts will be focused on examining a subset of chemokines and receptors that can modulate migration of these T lymphocytes. Murine tuberculosis models, as well as immunohistochemical, laser microdissection, and realtime PCR techniques will be used to characterize the expression of these specific chemokines and receptors during tuberculous infection. Mice with disruption of specific chemokine receptor genes and ligand neutralizing reagents will be exploited to dissect specific chemokine network. Similar techniques, in conjunction with in vitro cell migration assays and the TNF-alpha neutralization model of murine reactivation tuberculosis, will be employed to evaluate the effects of TNF-alpha on the expression of specific chemokines and receptors, as well as on migration of T cells and monocytes during tuberculous infection. These studies should yield valuable information that will shed light on the roles of chemokines and receptors on cell migration, granuloma formation, and host defense in tuberculous infection.